Store and stream task execution logs

[zaychenko-sergei]

Introduce TaskExecutionLogStore component:
- Associates a log file with a Task ID
- Each file is a stream of structured log entry records (perhaps, in a format like NDJSON) - each record contains information about the components issuing it, traces/spans …
- Import and save log files as task progresses / completes

Initial simplest implementation:
- storage an in-memory hash table with task ID as a key
- store log files collection as an in-memory file in a format convenient for quick skipping (like NDJSON)
lost after server restart
- Have a time-based automatic purging of old logs - i.e. N=30 days max
- Future: Store logs as S3
- Future: Maybe something like ELK stack, if further analytics will be necessary

GraphQL API:
- Allow downloading / viewing full log files / viewing parts (paging by log entries starting from the latest)
- Event time or log entry ID arebetter boundary than index for this type of pagination
- Filter log entries by log level
- A way to scroll quickly to given or relative time (1 hour ago, 3 hours ago, ..)